In electrical motors, the rotor normally includes a shaft which is supported at each end by bearings. The rotor itself may be formed on the shaft by, for example, pressing rotor laminations over the shaft to build up a suitable rotor. In switched reluctance machines, the rotor does not include wire coils as torque is generated by changing reluctance between the rotor and stator poles.
In certain switched reluctance machines, it may be desirable to eliminate one of the rotor bearings. In such a machine, the rotor shaft is mounted on a single bearing in a cantilever arrangement. In motors with a cantilevered rotor shaft, vibrations in the shaft are transmitted to the rotor. Vibrations in the rotor result in undesirable changes in the rotor-stator air gap and may, under certain conditions result in contact between the rotor and stator. It would, therefore, be advantageous to design a cantilevered rotor wherein the rotor would not, under normal operation conditions, contact the stator.
The present invention applies to any rotating electrical machine in which a rotor must be suspended from a single bearing, including electrical machines where the bearing is external to the machine. More particularly, the present invention is applicable to an electrical starter generator which is designed to be integrally mounted on the core engine rotor shaft in front of an engine bearing of a gas turbine engine.
Currently, all electrical machines are designed with a fixed rotor-to-stator air gap. The gap is minimized to achieve good machine efficiency, while avoiding interference between the rotor and stator. The gap is customarily sized to accommodate the displacement of the most severe vibrational mode.